Transmissions are devices that change the speed or torque of driving units that are mounted in automobiles, bicycles, etc. Transmissions are widely used in various forms in industrial and transport machines and general apparatus and mechanism fields that require a difference in speed between an input unit and an output unit.
In general, transmissions typically include a gear system, and implement a desired number of gear stages based on the gear ratio, i.e., the ratio of an input revolutions per minute (RPM) to an output RPM.
To adjust the ratio of an input RPM to an output RPM, there is a need for a configuration for controlling the relationships between gears. However, this configuration is disposed outside an input shaft or a rotating shaft and, thus, increases the size of a transmission and makes the structure thereof complicated.